Ozone is generated industrially for application in a number of industrial processes, particularly in water treatment and purification processes. Ozone gas can be used as a replacement for chlorine in many water treatment applications that result in the elimination of harmful chlorinated byproducts. Ozone can also be used as a bleaching agent for products such as clays, pulps, and textiles; an oxidant in both organic and inorganic reactions; a bactericide; and a pharmaceutical intermediate. A gasified ozone beam can be used in processes performed under vacuum, such as the formation of thin films and etching processes.
Ozone is a metastable allotrope of oxygen, and therefore breaks down into molecular oxygen in a relatively short period of time. Furthermore, gaseous ozone in concentrations above 20% can be explosive when it comes in contact with reactive materials such as organic material, ceramic containers, and so forth. As a result, ozone cannot be practically stored and must be generated on site. The high cost of the required ozone generator and ancillary equipment is a significant limiting factor in the use of ozonation technology.
Ozone is generated industrially in most cases by passing a process gas, typically anhydrous oxygen, through a corona discharge. Industrial corona discharge generators typically produce 6% (by weight) ozone when supplied with anhydrous oxygen as the feed gas. The gas mixture exiting the ozone generator, consisting of 6% ozone and 94% oxygen, is typically fed directly into the process fluid. There is usually no provision made for oxygen recovery, resulting in extremely wasteful use of the oxygen. Due to the high level of oxygen waste with this type of system, a tremendous amount of costly oxygen is required to produce relatively small amounts of ozone gas.
Regarding ozone transfer into a process fluid stream, there are certain limitations due to the low conversion rates of oxygen to ozone currently attainable. Henry's Law holds that the solubility of a gas is directly proportional to the partial pressure of the gas above the solution. That is, the more dilute the ozone in the gas mixture, the less ozone will tend to enter into solution. Therefore, even though ozone is 12.5 times more soluble in water than oxygen, transfer of ozone into the process fluid stream is not as readily accomplished as its solubility would indicate due to the low (typically about 6% ) concentration of ozone gas attainable with current ozone generation processes. Ozone tends to stay in the gas mixture and ozone waste results. In fact, many ozone applications have ozone destruct equipment installed to destroy expensively generated ozone that has not gone into solution after being injected into the process fluid stream. Eliminating nonreactive carrier gases from the ozone/water interface can essentially eliminate waste of ozone resulting from Henry's Law limitations if the ozone is efficiently injected, and its endpoint concentration is below the equilibrium concentration of pure ozone in the process fluid.
In addition to Henry's Law, the process fluid's temperature and its content of ozone reactive material affects the solubility of ozone. When ozone reactive materials are present in fairly large quantities, ozone mass transfer efficiencies are increased and Henry's Law is no longer the dominant factor in the amount of ozone gas entering into solution in the process fluid. Total ozone consumption increases because the ozone reacts very quickly with the ozone reactive materials. Process fluid temperature also affects ozone mass transfer. As the temperature of the process fluid increases, the solubility of ozone in the process fluid decreases. Process fluid streams in excess of 54.degree. C. are generally avoided in industry. Regardless, whenever nonreactive carrier gases are present in the gas injected into the process fluid, ozone mass-transfer rates and quantities are still affected by Henry's Law. Eliminating nonreactive carrier gases will reduce ozone waste. In the case of higher temperature applications eliminating nonreactive carrier gases will increase ozone mass-transfer rates into the process fluid, which will make more practical the sizing of contacting equipment.
Ozone processing of fluids are an important attribute to industry, but many are limited by inefficient use of oxygen, and unnecessary waste of ozone. What is needed is an efficient and economical continuous process and apparatus for: generating liquid ozone; recycling unused anhydrous oxygen; and eliminating nonreactive carrier gases in the injection equipment.